S100 is definitely more pocketable than the RX-100.S100 UI is easier to use and navigate than RX-100.S100 is much cheaper than RX-100.

RX-100 is better at low light.RX-100 IQ is MUCH better.RX-100 feature set improves the functionally of this P&S.

In summary: RX-100 goes in the bag. S100 sits alone on the shelf.

or, if you have S100 and you just like facebook-worthy pictures and you just want to have a pocketable camera. RX100 I think is more comparable to G11/G12 though it's smaller. For me, a S100 / DSLR combo is still hard to beat. Where S100 fails, you have the DSLR to cover it. Of course, no one is stopping you if you have the money to buy an RX100. But for me, I'd rather use the extra money in pampering my DSLR with better lenses.

It does work in broad daylight but I was referring to fast moving objects where I would need the AF speed of a DSLR.

Gotcha.

Actually I was trying to shoot some clouds out of an airplane window & the RX100 just wouldn't focus. I thought the clouds had enough contrast to focus easily... but it was extremely difficult.

Maybe any compact would've had trouble; I'm not sure. I really do love the RX100. The bounce-flash, the larger sensor, the longer focal length lens for equivalent FOV compared to S100 guarantees that your diffraction-limited aperture is higher (e.g. f/4-f/5.6) --making those smaller apertures actually useful, the contrast of the lens (in the center anyway), etc.